The present invention relates to an improved hot stamping foil, more particularly to a hot stamping foil having a layer which includes a thermochromic compound and an antimicrobial compound.
Various systems for transferring ink images onto a substrate, such as a fabric or an article of manufacture, are known. For example, images can be transferred from a heat transfer sheet by the use of heat and pressure. Such sheets (also known as hot-stamp foils) are shown, for example, in U.S. Pat. No. 5,124,309, to Egashira, and U.S. Pat. No. 5,223,476, to Kanto et al.
More complex systems for transferring images are shown, for example, in U.S. Pat. No. 5,244,524, to Yamane. Yamane describes an ink image forming step in which an ink image is formed on a hot melting type adhesive layer of a transfer sheet, followed by an image retransferring step in which the ink image and the hot melting type adhesive layer are transferred onto the substrate by application of heat and pressure.
Various inks and dyes have been employed in known heat transfer sheets or hot-stamp foils. For certain applications, it would be desirable to employ a so-called thermochromic compound, that is, a compound which changes color (typically from colored to colorless or vice versa) at a specified transition temperature. Images so formed can, for example, provide an indication of the temperature of the substrate to which they are applied, or can provide a decorative effect.
Once an image is transferred to a medium, it becomes susceptible to attack by microbes. These microbes feed on the image and the surrounding medium; if present in sufficient numbers, they degrade the appearance of the image and can degrade even the medium itself. One can address this problem by transferring an image to a fabric coated with an antimicrobial agent, as is taught by Rubin et al in U.S. Pat. No. 5,565,265. The fabric thus coated is said to be effective in retarding the growth of microbes.
In a similar manner, one can incorporate an antimicrobial compound directly into plastic products to retard the growth of microbes. The typical method mixes a preservative with the plastic before the plastic is molded or rolled into a sheet. This method has its drawbacks, however. Certain plastics, such as polystyrene, may inhibit the effectiveness of the antimicrobial compound. This method is moreover wasteful: in all molded plastic items, a large proportion of the antimicrobial compound used is unavailable because it is sealed within the plastic. This large proportion is not exposed to the surface, where microbes attack.
It would be desirable to provide an improved hot-stamp foil comprising a layer which includes a thermochromic compound, and preferably a thermochromic layer which provides a reversible thermochromic effect. It would be further desirable to impart microbial resistance to an image transferred by the improved hot-stamp foil.
In accordance with one aspect of the present invention, there has been provided a hot stamping foil comprising a carrier, and disposed thereon, a thermochromic layer comprising a mixture of a thermochromic compound, a sizing or adhesive compound, a release compound, and a antimicrobial compound.
In accordance with another aspect of the present invention, a method of producing a hot stamping foil is provided which comprises the steps of: preparing a thermochromic mixture comprising a thermochromic compound, a sizing or adhesive compound, a release compound, and an antimicrobial compound; and applying to a carrier layer a layer of the thermochromic mixture.
According to a further aspect of the present invention, an article of manufacture is provided comprising a substrate and, applied thereto, a hot stamping foil as described above.
According to yet another aspect of the present invention, a method of labeling an article of manufacture is provided comprising the steps of: contacting the thermochromic layer of the hot stamping foil described above with the article; hot stamping the hot stamping foil to cause the thermochromic layer to adhere to the article; and removing the carrier of the hot stamping foil from the thermochromic layer.
The hot stamping foil of the present invention may be applied to a variety of plastics, even to many plastics which inhibit the effectiveness of the antimicrobial compound, and may also be applied to other items that are not made of plastic such as wood, paper, and leather.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.